diff --git a/denotational-design-tutorial.md b/denotational-design-tutorial.md
new file mode 100644
index 0000000000..a7608c254c
--- /dev/null
+++ b/denotational-design-tutorial.md
@@ -0,0 +1,240 @@
+# Denotational Design: Part 1
+
+## The Basic Idea
+
+Denotational design means designing an abstraction by first asking:
+
+> What does this thing mean?
+
+Before choosing data structures, algorithms, callbacks, queues, caches, or runtime behavior, we give each core type a simple meaning. Then we define operations in terms of that meaning.
+
+The implementation can be clever later. The meaning should be simple now.
+
+## API vs Implementation vs Meaning
+
+When designing a library, there are three related but different things:
+
+| Layer | Question | Example |
+| --- | --- | --- |
+| API | What can users call? | `map(signal, f)` |
+| Implementation | How does it run? | subscriptions, graphs, caching |
+| Denotation | What does it mean? | a value changing over time |
+
+Most designs jump between API and implementation. Denotational design adds the missing middle: a precise meaning.
+
+## A Tiny FRP Example
+
+Functional Reactive Programming is a good example because it starts with a very simple denotation.
+
+A time-varying value, often called a `Behavior`, can be understood as:
+
+```ts
+Behavior<A> = Time -> A
+```
+
+That says:
+
+> A `Behavior<A>` means: give me a time, and I can tell you the `A` value at that time.
+
+This does not mean the implementation literally stores an infinite function. It means this is the specification. The implementation may use events, subscriptions, incremental recomputation, dependency graphs, or caching.
+
+## Operations Follow From Meaning
+
+Once we know what `Behavior<A>` means, operations become easier to define.
+
+For example, `map` transforms the value inside a behavior:
+
+```ts
+map: (A -> B) -> Behavior<A> -> Behavior<B>
+```
+
+Its meaning is:
+
+```ts
+map(f, behavior)(time) = f(behavior(time))
+```
+
+That is the whole specification.
+
+Similarly, a constant behavior:
+
+```ts
+constant: A -> Behavior<A>
+```
+
+means:
+
+```ts
+constant(value)(time) = value
+```
+
+The definitions are simple because the denotation is simple.
+
+## Why This Helps
+
+Denotational design is useful because it separates essence from machinery.
+
+It helps library users because the abstraction has a clear mental model.
+
+It helps implementers because correctness has a target independent of implementation details.
+
+It helps API design because awkward operations become easier to spot. If an operation has no clean meaning, it may be exposing implementation machinery instead of domain meaning.
+
+## The Design Loop
+
+A practical denotational design loop looks like this:
+
+1. Name the core type.
+2. Write down what values of that type mean.
+3. Define each operation by how it transforms meanings.
+4. Notice what laws naturally follow.
+5. Choose an implementation that preserves the meaning.
+
+The key discipline is to delay implementation concerns until after the meaning is clear.
+
+## Denotation Is Not Implementation
+
+A denotation can look like an implementation because it is concrete enough to write down:
+
+```ts
+Behavior<A> = Time -> A
+```
+
+But this equation is not saying that a real FRP system must store a function from every possible time to an `A` value.
+
+It is saying that this is the model we use to understand a behavior.
+
+The implementation might use callbacks, mutable cells, event queues, dependency graphs, caching, sampling, or incremental recomputation. Those choices are representation. The denotation is the meaning those representations must preserve.
+
+So there are two different questions:
+
+| Question | Answer |
+| --- | --- |
+| What does a behavior mean? | A function from time to value |
+| How do we run it efficiently? | Some concrete representation and algorithm |
+
+A denotation should be simple and precise. An implementation should be executable and efficient. They do not have to be the same thing.
+
+## Operations At Two Levels
+
+Conal Elliott describes a useful pattern:
+
+> The meaning of each method corresponds to the same method for the meaning.
+
+This sentence is subtle because there are three things in play:
+
+1. An abstract type, like `Behavior<A>`.
+2. A meaning type, like `Time -> A`.
+3. A meaning function that translates from the abstract type to the meaning type.
+
+For behaviors, Conal often calls the meaning function `at`:
+
+```ts
+at: Behavior<A> -> (Time -> A)
+```
+
+Read this as:
+
+> `at(behavior)` gives the meaning of `behavior`.
+
+So `at` is just the specific FRP name for the more general idea:
+
+```ts
+meaning: Abstract<A> -> Model<A>
+```
+
+Now we can talk about operations.
+
+There are two versions of "the same" operation.
+
+One operation belongs to the abstract API:
+
+```ts
+mapBehavior: (A -> B) -> Behavior<A> -> Behavior<B>
+```
+
+The other operation belongs to the semantic model:
+
+```ts
+mapFunction: (A -> B) -> (Time -> A) -> (Time -> B)
+```
+
+They are not literally the same function. They live at different levels. But they are the same conceptual operation: mapping a pure function over a value inside some structure.
+
+The homomorphism law says that translating meanings should not care which order we take these steps.
+
+Path 1: operate first, then take the meaning.
+
+```ts
+behavior
+  -> mapBehavior(f, behavior)
+  -> at(mapBehavior(f, behavior))
+```
+
+Path 2: take the meaning first, then operate on the meaning.
+
+```ts
+behavior
+  -> at(behavior)
+  -> mapFunction(f, at(behavior))
+```
+
+The law says both paths produce the same meaning:
+
+```ts
+at(mapBehavior(f, behavior))
+=
+mapFunction(f, at(behavior))
+```
+
+Using the generic word `meaning`, the same law is:
+
+```ts
+meaning(operationOnAbstraction(x))
+=
+operationOnMeaning(meaning(x))
+```
+
+In pointwise form:
+
+```ts
+at(mapBehavior(f, behavior))(time)
+=
+f(at(behavior)(time))
+```
+
+So the operation on the abstraction must mean the corresponding operation on the model.
+
+That is the homomorphism idea: the meaning function preserves structure. It translates the abstract operation into the corresponding model operation.
+
+```ts
+// Same shape, different levels:
+
+mapBehavior(f, behavior)       // abstract level
+
+mapFunction(f, at(behavior))   // meaning/model level
+
+// Connected by the meaning function:
+
+at(mapBehavior(f, behavior))
+=
+mapFunction(f, at(behavior))
+```
+
+This gives us a correctness rule. If `Behavior` claims to support `map`, its `map` should behave like `map` on its denotation, which is a function of time.
+
+## The Main Lesson
+
+Denotational design does not ask, "How do we build this?" first.
+
+It asks:
+
+> What are we talking about?
+
+For FRP, the answer begins with:
+
+```ts
+Behavior<A> = Time -> A
+```
+
+That small equation gives the abstraction a center of gravity. Everything else can be designed around it.
diff --git a/packages/opencode/src/cli/cmd/tui/app.tsx b/packages/opencode/src/cli/cmd/tui/app.tsx
index c7a2cd560f..25d4a37df3 100644
--- a/packages/opencode/src/cli/cmd/tui/app.tsx
+++ b/packages/opencode/src/cli/cmd/tui/app.tsx
@@ -275,6 +275,7 @@ function App(props: { onSnapshot?: () => Promise<string[]> }) {
   }
 
   const api = createTuiApi({
+    command,
     tuiConfig,
     dialog,
     keymap,
diff --git a/packages/opencode/src/cli/cmd/tui/plugin/api.tsx b/packages/opencode/src/cli/cmd/tui/plugin/api.tsx
index 7b7ce0bbb5..9f9848cf75 100644
--- a/packages/opencode/src/cli/cmd/tui/plugin/api.tsx
+++ b/packages/opencode/src/cli/cmd/tui/plugin/api.tsx
@@ -1,4 +1,10 @@
-import type { TuiDialogSelectOption, TuiPluginApi, TuiRouteDefinition, TuiSlotProps } from "@opencode-ai/plugin/tui"
+import type {
+  TuiCommand,
+  TuiDialogSelectOption,
+  TuiPluginApi,
+  TuiRouteDefinition,
+  TuiSlotProps,
+} from "@opencode-ai/plugin/tui"
 import type { useEvent } from "@tui/context/event"
 import type { useRoute } from "@tui/context/route"
 import type { useSDK } from "@tui/context/sdk"
@@ -17,6 +23,7 @@ import { Slot as HostSlot } from "./slots"
 import type { useToast } from "../ui/toast"
 import { InstallationVersion } from "@opencode-ai/core/installation/version"
 import * as Keymap from "../keymap"
+import type { useCommandPalette } from "../context/command-palette"
 
 type RouteEntry = {
   key: symbol
@@ -26,6 +33,7 @@ type RouteEntry = {
 export type RouteMap = Map<string, RouteEntry[]>
 
 type Input = {
+  command: ReturnType<typeof useCommandPalette>
   tuiConfig: TuiConfig.Resolved
   dialog: ReturnType<typeof useDialog>
   keymap: ReturnType<typeof useOpencodeKeymap>
@@ -41,6 +49,54 @@ type Input = {
   renderer: TuiPluginApi["renderer"]
 }
 
+let warnedLegacyCommand = false
+
+function warnLegacyCommandApi() {
+  if (warnedLegacyCommand) return
+  warnedLegacyCommand = true
+  console.warn("[tui.plugin] api.command is deprecated; use api.keymap.registerLayer({ commands, bindings }) instead")
+}
+
+function commandBinding(command: TuiCommand, input: Input) {
+  if (!command.keybind) return []
+  return input.tuiConfig.keybinds.get(command.keybind).map((binding) => ({ ...binding, cmd: command.value }))
+}
+
+function legacyCommandApi(input: Input): TuiPluginApi["command"] {
+  return {
+    register(cb) {
+      warnLegacyCommandApi()
+      const list = cb()
+      return input.keymap.registerLayer({
+        commands: list.map((command) => ({
+          name: command.value,
+          title: command.title,
+          desc: command.description,
+          category: command.category,
+          namespace: "palette",
+          suggested: command.suggested,
+          hidden: command.hidden,
+          enabled: command.enabled,
+          slashName: command.slash?.name,
+          slashAliases: command.slash?.aliases,
+          run() {
+            command.onSelect?.()
+          },
+        })),
+        bindings: list.flatMap((command) => commandBinding(command, input)),
+      })
+    },
+    trigger(value) {
+      warnLegacyCommandApi()
+      input.keymap.dispatchCommand(value)
+    },
+    show() {
+      warnLegacyCommandApi()
+      input.command.show()
+    },
+  }
+}
+
 function routeRegister(routes: RouteMap, list: TuiRouteDefinition[], bump: () => void) {
   const key = Symbol()
   for (const item of list) {
@@ -209,6 +265,7 @@ export function createTuiApi(input: Input): TuiPluginApi {
       },
     },
     keymap: input.keymap,
+    command: legacyCommandApi(input),
     route: {
       register(list) {
         return routeRegister(input.routes, list, input.bump)
diff --git a/packages/opencode/src/cli/cmd/tui/plugin/runtime.ts b/packages/opencode/src/cli/cmd/tui/plugin/runtime.ts
index 91ccaaaa01..3c5d3eaa1b 100644
--- a/packages/opencode/src/cli/cmd/tui/plugin/runtime.ts
+++ b/packages/opencode/src/cli/cmd/tui/plugin/runtime.ts
@@ -563,6 +563,18 @@ function pluginApi(runtime: RuntimeState, plugin: PluginEntry, scope: PluginScop
 
   const keymap = createScopedKeymap(api.keymap, scope)
 
+  const command: TuiPluginApi["command"] = {
+    register(cb) {
+      return scope.track(api.command.register(cb))
+    },
+    trigger(value) {
+      api.command.trigger(value)
+    },
+    show() {
+      api.command.show()
+    },
+  }
+
   let count = 0
 
   const slots: TuiPluginApi["slots"] = {
@@ -578,6 +590,7 @@ function pluginApi(runtime: RuntimeState, plugin: PluginEntry, scope: PluginScop
     app: api.app,
     keys: api.keys,
     keymap,
+    command,
     route,
     ui: api.ui,
     tuiConfig: api.tuiConfig,
diff --git a/packages/opencode/test/cli/tui/plugin-loader.test.ts b/packages/opencode/test/cli/tui/plugin-loader.test.ts
index d62bc19bfe..f83e741a85 100644
--- a/packages/opencode/test/cli/tui/plugin-loader.test.ts
+++ b/packages/opencode/test/cli/tui/plugin-loader.test.ts
@@ -776,6 +776,79 @@ test("auto-disposes plugin keymap layers", async () => {
   }
 })
 
+test("supports legacy plugin command API", async () => {
+  await using tmp = await tmpdir({
+    init: async (dir) => {
+      const file = path.join(dir, "legacy-command-plugin.ts")
+      const spec = pathToFileURL(file).href
+      const marker = path.join(dir, "legacy-command.txt")
+
+      await Bun.write(
+        file,
+        `export default {
+  id: "demo.command.legacy",
+  tui: async (api) => {
+    api.command.register(() => [{
+      title: "Legacy command",
+      value: "demo.command.legacy.run",
+      onSelect() {
+        Bun.write(${JSON.stringify(marker)}, "called")
+      },
+    }])
+    api.command.trigger("demo.command.legacy.run")
+    api.command.show()
+  },
+}
+`,
+      )
+
+      return { spec, marker }
+    },
+  })
+
+  let add = 0
+  let drop = 0
+  let show = 0
+  const wait = spyOn(TuiConfig, "waitForDependencies").mockResolvedValue()
+  const cwd = spyOn(process, "cwd").mockImplementation(() => tmp.path)
+
+  try {
+    await TuiPluginRuntime.init({
+      api: createTuiPluginApi({
+        command: {
+          register(cb) {
+            add += 1
+            const list = cb()
+            return () => {
+              drop += list.length
+            }
+          },
+          trigger(value) {
+            expect(value).toBe("demo.command.legacy.run")
+            Bun.write(tmp.extra.marker, "called")
+          },
+          show() {
+            show += 1
+          },
+        },
+      }),
+      config: createTuiResolvedConfig({
+        plugin: [tmp.extra.spec],
+        plugin_origins: [{ spec: tmp.extra.spec, scope: "local", source: path.join(tmp.path, "tui.json") }],
+      }),
+    })
+
+    expect(add).toBe(1)
+    expect(show).toBe(1)
+    await expect(fs.readFile(tmp.extra.marker, "utf8")).resolves.toBe("called")
+  } finally {
+    await TuiPluginRuntime.dispose()
+    expect(drop).toBe(1)
+    cwd.mockRestore()
+    wait.mockRestore()
+  }
+})
+
 test("plugin keymap proxy preserves real keymap receiver", async () => {
   await using tmp = await tmpdir({
     init: async (dir) => {
diff --git a/packages/opencode/test/fixture/tui-plugin.ts b/packages/opencode/test/fixture/tui-plugin.ts
index 62a3ae6e6b..342ea0b225 100644
--- a/packages/opencode/test/fixture/tui-plugin.ts
+++ b/packages/opencode/test/fixture/tui-plugin.ts
@@ -82,6 +82,7 @@ function themeCurrent(): HostPluginApi["theme"]["current"] {
 
 type Opts = {
   client?: HostPluginApi["client"] | (() => HostPluginApi["client"])
+  command?: Partial<HostPluginApi["command"]>
   renderer?: HostPluginApi["renderer"]
   count?: Count
   keymap?: HostPluginApi["keymap"]
@@ -131,6 +132,7 @@ export function createTuiPluginApi(opts: Opts = {}): HostPluginApi {
         ? () => opts.client as HostPluginApi["client"]
         : fallback
   const client = () => read()
+  const commands: ReturnType<Parameters<HostPluginApi["command"]["register"]>[0]> = []
   let depth = 0
   let size: "medium" | "large" | "xlarge" = "medium"
   const has = opts.theme?.has ?? (() => false)
@@ -187,6 +189,25 @@ export function createTuiPluginApi(opts: Opts = {}): HostPluginApi {
       formatSequence: () => "",
       formatBindings: () => undefined,
     },
+    command: {
+      register(cb) {
+        if (opts.command?.register) return opts.command.register(cb)
+        const list = cb()
+        commands.push(...list)
+        if (count) count.command_add += 1
+        return () => {
+          if (count) count.command_drop += 1
+          commands.splice(0, commands.length, ...commands.filter((command) => !list.includes(command)))
+        }
+      },
+      trigger(value) {
+        if (opts.command?.trigger) return opts.command.trigger(value)
+        commands.find((command) => command.value === value)?.onSelect?.()
+      },
+      show() {
+        opts.command?.show?.()
+      },
+    },
     get client() {
       return client()
     },
diff --git a/packages/plugin/src/tui.ts b/packages/plugin/src/tui.ts
index 13bc17f66b..946a8d6736 100644
--- a/packages/plugin/src/tui.ts
+++ b/packages/plugin/src/tui.ts
@@ -70,6 +70,23 @@ export type TuiRouteDefinition = {
   render: (input: { params?: Record<string, unknown> }) => JSX.Element
 }
 
+/** @deprecated Use api.keymap.registerLayer({ commands, bindings }) instead. */
+export type TuiCommand = {
+  title: string
+  value: string
+  description?: string
+  category?: string
+  keybind?: string
+  suggested?: boolean
+  hidden?: boolean
+  enabled?: boolean
+  slash?: {
+    name: string
+    aliases?: string[]
+  }
+  onSelect?: () => void
+}
+
 export type TuiKeys = {
   formatSequence: (parts: readonly KeySequenceFormatPart[] | undefined) => string
   formatBindings: (bindings: readonly SequenceBindingLike[] | undefined) => string | undefined
@@ -463,6 +480,12 @@ export type TuiPluginApi = {
   app: TuiApp
   keys: TuiKeys
   keymap: TuiKeymap
+  /** @deprecated Use api.keymap.registerLayer({ commands, bindings }) instead. */
+  command: {
+    register: (cb: () => TuiCommand[]) => () => void
+    trigger: (value: string) => void
+    show: () => void
+  }
   route: {
     register: (routes: TuiRouteDefinition[]) => () => void
     navigate: (name: string, params?: Record<string, unknown>) => void